Tinnitus describes a perceived sound, e.g., ringing, buzzing, whistling, or roaring, that is experienced by a tinnitus sufferer and that does not exist as a physical sound. The condition can be annoying or very painful, and the discomfort caused by tinnitus frequently interferes with a sufferer's sleep. Tinnitus often occurs at a specific frequency or over a small frequency range and is frequently constant; however, the specific frequency or small frequency range varies from patient to patient.
Most of the relatively recent efforts to treat tinnitus have involved attempts to mask the perceived sound. Masking is the interference of one sound on another. Perfect tinnitus masking involves providing a masking signal that exactly overrules the perceived sound in terms of psychoacoustics without supplying unnecessary energy to the tinnitus sufferer. See e.g., Tinnitus: Diagnosis/Treatment 55 (Abraham Shulman ed. 1991).
Many conventional tinnitus maskers produce only a broad band masking noise or signal. The masking signal produced by these conventional maskers is elevated to a level adequate to mask the tinnitus, but the energy supplied to the tinnitus sufferer's ear is considerably in excess of the required amount. Even if a masker is custom made to be near the sufferer's tinnitus frequency, the broad masking signal supplies energy at many other frequencies as well.
In 1981, the Committee on Hearing, Bioacoustics, and Biomechanics of the National Academy of Science presented characteristics that the committee felt were needed in future tinnitus maskers. The recommendations included a masker that would use narrow bands of noise to reduce the energy delivered, that would match the tinnitus frequency, and that would include a variable bandwidth for the masking frequencies. See H. Sauberman, Report on Tinnitus Working Group No. 89 of CHABA, Second International Tinnitus Seminar 250-52 (A. Shulman, J. Ballantine, and J. Laryngol eds. suppl. 1981).
Thus a need has arisen for a tinnitus masker that uses a minimal amount of energy, that allows for a variable center frequency of the masking signal over the human auditory spectrum including high frequencies, and that provides for variable bandwidth selection.